Current air filtration devices for use in the home generally are stand alone units having a single enclosure containing one or more filters through which air is drawn and from which the filtered air exits radially at high speeds. These devices are rated, based on the amount and rate at which air is filtered, as cubic feet per minute (CFM). Using a standard size room as a basis, a rating for an air filter is usually given as "room air changes per hour" which is derived from the CFM ratio. However, despite the suggestion that all the air in a room is cleaned several times per hour, only the air exiting from the device is truly clean. For illustration, unfiltered air, being drawn towards the air intake port, is continuously contaminating the filtered air exiting from the same device. Therefore, even if one of these currently available filtration devices is placed in a bedroom, a person sleeping in a bed in the room is not actually breathing clean, filtered air, but rather is breathing air that is only somewhat cleaner than air that is wholly unfiltered.
Moreover, current filtration devices are highly inefficient because, as single, stand alone units, at least some of the filtered air exiting radially from these devices is being drawn directly back into the intake ports. Location of the device then becomes an important factor with current devices. Rather than cleaning all the air in a given room, these devices tend to inefficiently refilter the same air in a portion of the room over and over again. Although these devices can be placed alongside or at the foot of a bed, they do not deliver truly clean air to someone lying in the bed. Unless a room is air tight, which virtually all rooms are not, air borne contaminants are constantly being replenished by outside, unfiltered air.
Furthermore, the ability of these devices to clean more air at a faster rate is dependent on the power and speed of the fans employed in the devices. Thus the noise level of these fans, especially with the larger units, renders these devices unsuitable for use while a person is sleeping. In addition, dust mites and other allergens associated with mattresses, pillows and bed linens may not be filtered at all by current filtration devices.